Heat exchangers are widely used, for instance in the power supply and chemical industries, and for marine applications. A plurality of tubes, typically linear, are mounted in tube plates, being connected in parallel between "headers" so as to carry heat exchanger fluid, though heat exchangers are known with a single header and "U" shaped tubes.
Generally, the tubes will carry the coolant, typically air or water (perhaps sea water), and the fluid which is to be cooled is circulated around the tubes,.
If one or more of the tubes develops a leak, with leakage of the fluid being cooled, for example hot oil, into the coolant, then to prevent the oil being discharged with the coolant e.g. for marine applications into the sea, each defective tube needs to be taken out of service (by being "plugged"), for instance until the ship reaches port and the tube can be replaced.
Heat exchanger tubes conventionally have thin walls in order to maximise heat transfer. Such thin walls require special care to prevent damage by the fitted tube plug. Following prolonged heat exchanger use, the terminal end of a tube (and the area immediately inwards of this terminal end) can become non-uniform, by one or more of erosion, corrosion and contaminant build-up, making it difficult to ensure effective sealing.